new c++
MyClass * p1 = new MyClass;
// allocates memory by calling: operator new (sizeof(MyClass))
// and then constructs an object at the newly allocated space
MyClass * p2 = new (std::nothrow) MyClass;
// allocates memory by calling: operator new (sizeof(MyClass),std::nothrow)
// and then constructs an object at the newly allocated space
new (p2) MyClass;
// does not allocate memory -- calls: operator new (sizeof(MyClass),p2)
// but constructs an object at p2
// Notice though that calling this function directly does not construct an
//object:
MyClass * p3 = (MyClass*) ::operator new (sizeof(MyClass));
// allocates memory by calling: operator new (sizeof(MyClass))
// but does not call MyClass's constructor
delete p1;
delete p2;
delete p3;